How can I blend a matcap material with a texture
Ok, so I've found an acceptable workaround thanks to Gandalf3's comment to the question, which references another question that asks how regular materials can be made to work like a matcap. Here is how I set up my material to get both a texture using the main UV map, and camera dependent shading, by blending it with a matcap.



These steps assume you have already created a material and assigned a texture to it in the first (top) texture slot. Also, make sure you are using the GLSL display mode ('n' to open display panel, then select from the 'Shading' section) and are viewing in textured mode ('alt + z'). You needn't have any lights in your scene for this to work.


Check the material's 'Shadeless' parameter. We don't want lighting, because the matcap will be assigned to provide a faked lighting effect that is dependent on the surface normal relative to the camera.





Add a new texture in slot 2 (below slot 1) and assign a matcap texture. You can find some matcap textures here: https://svn.blender.org/svnroot/bf-blender/trunk/blender/release/datafiles/matcaps/





Set the coordinates of the matcap to 'Normal' in the 'Mapping' section of the texture properties. If you look in the viewport now, it will appear like a regular matcap in shaded mode.
The matcap needs to be blended with the texture, so set the 'Blend' parameter in the 'Influence' section to 'Multiply'.


If you have done this correctly, when you move the camera around, the matcap should provide some kind of lighting to the model, allowing you to see the shape of the model with the texture applied much more clearly. Note that you may need to adjust the matcap to make the lighting effect more obvious. I used the default Blender matcap (mc01.jpg from the link above) and increased the contrast in an image editor to get darker shading.